This is a program project grant proposal which involves a series of studies that concern major current problems in the carcinogenic action of important environmental (including occupational) agents by the inhalation route. These studies deal with mechanisms of action of carcinogens, development of animal modes, dose effect relationships, and interactions of environmentally important agents in the carcinogenic process. The six proposed studies involve the relationship of structure to carcinogenic function of acylating agents, the cocarcinogenic action of catechol and benzo(a)pyrene, the development of an animal model for leukemogenesis by benzene and lung cancer by arsenic trioxide, the carcinogenic interaction of hydrogen chloride and formaldehyde, and the relationships of fiber length to the inhalation carcinogenicity of asbestos. The proposal also includes support for Core Unit to operate the inhalation facility and renovation to upgrade the safety of carcinogen handling in the inhalation facility.